2.5 Description of the Applied Propagation Models
3.1.3 Energy efficiency analysis
Power consumption model for Macrocell base station
For evaluating the energy efficiency of different levels of macrocellular densification, a correct estimation of area power consumption is imperative which depends on the acurate modeling of the power consumption of an individual base station. The power consumption model for macrocellular base station, proposed in [85], considers the impact of external and internal components of the base station power consumption while at the same time also taking into account the impact of hourly network load.
As such the power consumption of a macro base station site,PBSM acro, is given by:
PBSM acro[W] =Pconst+Pload·F (3.5) where Pconst is the total load-independent power contribution stemming from recti-fier,PRect, microwave link for backhaul connectivity,PM Link, and site air conditioning unit,PAir−Cond, as given in (3.6). Pload, in turn, is the total load-dependent power consumption share stemming from power amplifier, PAmp, transceiver, PT RX, and digital signal processing units,PDSP, as given in (3.7). F is the load factor, varying between 0 (no load) and 1 (high/peak load). As the network is assumed to be oper-ating at full load, i.e., all the base stations transmitting at full power, thereforeF is assumed to be 1.
Pconst[W] = (nsect·PRect) +PM Link+PAir−Cond (3.6) Pload[W] =nsect·[PAmp+PT RX+PDSP] (3.7) In general, the contributions of PAmp,PT RX andPRectscale with the number of sectors,nsector, per base station site. The power consumption of the power amplifier, in turn, depends mainly on the input power requirements of the antenna,PT X and the power amplifier efficiency,ηAmp, and can be modelled and evaluated as:
PAmp= PT X
ηAmp (3.8)
Table 3.5 summarizes the input parameters for the macro base station power con-sumption model. The parameters are approximate values taken from [85], except for power amplifier efficiency. With the advancements in power amplifier (PA) technolo-gies e.g., Doherty PA with advanced signal conditioning algorithms, PA efficiencies in the range of 35 % to 65 % can be achieved when the network is operating in full
3.1. MACROCELLULAR DENSIFICATION 35
Table 3.5 Input parameters for the macrocellular BS power consumption model
Component/Equipment Unit Value
Number of sectors, 3
Transmit power at the antenna [Watts] 20
Power consumption of DSP card [Watts] 100
Power Amplifier efficiency [%] 45
Power consumption of Transceiver [Watts] 100 Power consumption of Rectifier [Watts] 100 Power consumption of Air-conditioning unit [Watts] 0 Power consumption of Microwave-Link unit [Watts] 80
load, as reported e.g. in [56, 108, 109], hence, a 45 % PA efficiency is asumed in the analysis. Moreover, new outdoor pole mounted BTS’s are also making their way into the markets, which don’t require power consuming air-conditioning [110]. Hence, a 0 Watt contribution is assumed from the air conditioning unit in this study. Based on the parameters in Table 3.5, the total power consumption of a macro base station can be evaluated yielding approximately 1113 W (∼1.11 kW). It is emphasized over here that many legacy macro-base stations can have still substantially higher total power consumption values, but the focus here is primarily on modern higher-efficiency equipment to understand the energy behavior of macro densification in the future.
Energy efficiency results and analysis
The power consumption per km2 increases with the increase in the cell density over an area. This is because the area power consumption depends on the coverage area of the base station. Using the input parameters from Table 3.5, the energy efficiency of macrocellular deployment with varying cell densities have been calculated using (2.5). Table 3.6 gives the area power consumption of pure macrocellular deployment with different cell densities. As one can note from the results, the power consumption per km2 increases with the increase in the cell density. In other words, densification of the network leads to increased power consumption per area proportionally with the increase in number of base stations. By densifying the network, the spectrum resources are reused more frequently, which thereby improves the network area spec-tral efficiency. However, looking at the impact of site densification on the energy efficiency of the network, as shown in Fig. 3.4, it is noted that although increasing the number of bps/Hz/km2, the energy needed to transmit 1 bps/Hz also increases as the network is densified, especially in the indoor environment. Considering the initial
Table 3.6 Area power consumption of pure macrocellular deployment over different ISDs
ISD ρcell Pkm2
[meters] [Cells per km2] [kW/km2]
960 3.8 1.4
828 5.1 1.9
593 9.9 3.7
297 39.3 14.5
170 119.9 44.4
0 20 40 60 80 100 120
3 4 5 6 7 8 9 10 11 12
Cell density [per km2]
Energyefficiency[bps/Hz/kW]
Outdoor Indoor
Base station power consumption = 1113 W
Figure 3.4 Energy efficiency [bps/Hz/kW] of pure Macrocellular network densifi-cation.
case of 3.8 cells/km2(ISD 960 m), where the average network area spectral efficiency is almost the same for both outdoor and indoor environment. In this case, the total power consumed per km2is approximately 1.4 kW, which leads to energy efficiency of approximately 10.8 bps/Hz/kW for outdoor and 10.7 bps/Hz/kW for indoor environ-ment. Upon decreasing the inter-site distance to 828 m (i.e., 5.1 cells/km2), a slight improvement can be observed in the energy efficiency (11.8 bps/Hz/kW for outdoor and 11.6 bps/Hz/kW for indoor). This improvement comes from the fact that in the initial stages of densification, the macrocellular network is slightly coverage limited.
Hence, by densifying the network, the coverage levels improve in both outdoor and indoor environment, thereby improving the radio channel conditions and hence per-mitting higher cell spectral efficiency. Subsequent densification down to ISD 593 m
3.1. MACROCELLULAR DENSIFICATION 37
Table 3.7 CAPEX and OPEX costs for macrocellular base station deployment CAPEX (Initial costs) Macrocell BS
Base station equipment 10 kAC
Site deployment cost 5 kAC
Total CAPEX 15 kAC
OPEX (Running costs) Macrocell BS Site rent (lease) 5 kAC/year Leased Line rent (backhaul) 2.25 kAC/year Operation and Maintenance 5 kAC/year Total OPEX 12.25 kAC/year
and 297 m starts to degrade the energy efficiency performance as the network becomes more and more interference limited. The impact of degradation is more visible in the indoor environment due to relatively low rate of spectral efficiency improvement as compared to the outdoor environment. Eventually, when the network is further den-sified to an extreme case (ISD 170 m case or 120 cells/km2), given approximately 32 times more cells/km2 as compared to initial ISD 960 m case, the area power con-sumption increases also increases proportionally (i.e. 32 times more). However at this stage, a slight improvement in the outdoor energy efficiency can be observed, but for the indoor environment the degradation in the energy efficiency performance extends even further. The reason is attributed to the indoor capacity inefficiency at this level of densification which is not able to offset the high area power consumption.